1. Field of the Invention
The present invention relates to a recording and reproducing apparatus for an optical disk capable of recording data on the optical disk and reading the data therefrom and, more particularly, relates to an erroneous recording prevention system for preventing the apparatus from making an erroneous recording/erasing operation while writing data.
2. Description of the Prior Art
An optical disk, which is provided with a recording medium, whose reflectance varies in response to light, formed on a recording surface of the optical disk and thereby enabled to record information and allow the information to be reproduced, is in practical use.
Such optical disk of an overwritable type is provided, for example, with a spiral track divided into n sectors S.sub.C1, S.sub.C2, S.sub.C3, . . . , S.sub.Cn as shown in FIG. 4, each sector having an address region AD.sub.1, AD.sub.2, AD.sub.3, . . . at the head portion thereof to record a piece of track address data therein. It is adapted such that, by irradiating the data recording area of each sector S.sub.C1, S.sub.C2, S.sub.C3, . . . by a laser beam modulated with recording data, the temperature at the irradiated portion is sharply elevated so that recording dots are formed there, or by throwing a laser beam weaker than that used at the time of recording on the recorded area, the information is read out.
Thus, it is arranged such that the laser beam irradiating the optical disk in the recording/erasing mode is provided with laser power several times as high as that for the laser beam in the reading mode. Hence, when the optical recording and reproducing apparatus in the recording/erasing mode was subjected to a strong vibration causing the laser beam to go off the recording/erasing track, such serious accidents sometimes occurred that the data already written in the track were destroyed or new data were written along an incorrect track of the optical disk.
Therefore, it has been considered to provide the apparatus with a component which monitors a tracking error signal and, when a detrack state is detected in the recording mode, the writing operation stops at once, thereby preventing the erroneous recording or erroneous erasing of data.
With the erroneous recording preventing device as described above, however, it sometimes occurs that the laser beam has already deviated a great degree from the on-track position when a detrack state is detected. Thus, there has been a problem with it that positive prevention of the erroneous recording/erasing cannot be assured.
More particularly, when the recording and reproducing apparatus for an optical disk is subjected to a strong shock, the focus servo sometimes comes off the control point, or it becomes unstable, before or at the same time as the detrack occurs. Then, the level of the tracking error signal itself may have already been lowered. Therefore, even if the tracking error signal is constantly monitored by a level comparison element or the like, it may be difficult to correctly detect occurrence of the detrack.
Further, when an out-of-focus state is brought about in the recording mode of erasing mode, the laser beam converged on the optical disk may be spread to cover other track regions and, hence, problems occur such that the recorded data on the optical disk are destroyed and, in the reading mode, many error data are produced.